1. Field of the Invention
The present invention relates to a linear light source. More specifically, it is directed to a linear light source comprising a plurality of luminous elements disposed in a straight line, and an apparatus capable of radiating reading light onto image recording media to read out images recorded thereon using said light source.
2. Description of the Related Art
In medical X-ray photography, an image reading system for reading out an electrophotografic latent image or electroradiographic image information has been proposed, in which a photoconductor made of an X-ray sensitive material, such as an a-Se selenium plate, is used as an electrophotografic recording medium to reduce an amount of dosage exposed to a subject and to improve diagnostic accuracy, and a radial ray, such as an X-ray which carries electroradiographic image information is radiated onto the medium to store charges of a latent image carrying the electroradiographic image information, which is subsequently read out by scanning the medium with a laser beam and detecting the current produced in the medium through flat plate or striped electrodes. (Refer to, for example, U.S. Pat. Nos. 4,176,275, 5,440,146 and 5,510,626 or a document entitled “A Method of Electronic Readout of Electrophotographic and Electroradiographic Image” on P 178 to 182 in the Journal of Applied Photographic Engineering, Volume 4, Number 4, Fall 1978.)
In the system described in the U.S. Pat. Nos. 4,176,275 and 5,510,626 or the aforementioned document, a linear narrow light beam formed by extending a light beam emitted from an argon laser is brought into focus on an electrophotografic medium with cylindrical lenses on the apparatus and is mechanically deflected to scan the medium, and the electrophotografic latent image recorded thereon is read out in parallel by wire electrodes disposed in stripes.
Also, the applicant has proposed a multi-layered electrophotografic recording medium which is layered in the order of a first electric conductor layer having permeability for radial rays, a recording photoconductive layer which takes on photoconductivity when exposed to a recording radial ray, a charge transport layer which behaves substantially as an insulator against charges having the same polarity with the charges charged on the first electric conductor layer and as an electric conductor for charges having the reverse polarity, a reading photoconductive layer which takes on photoconductivity when exposed to reading light, and a second electric conductor layer having permeability for the reading light; and an reading apparatus for reading out electroradiographic images recorded on the multi-layered electrophotografic recording medium. (Refer to, for example, U.S. Pat. No. 6,268,614.)
The reading apparatus described in U.S. Pat. No. 6,268,614 is an apparatus for reading out an electrophotografic latent image recorded on an electrophotografic recording medium by scanning the medium with the reading light radiated from a light source. For the reading light exposure apparatus which provides the light source for the reading light, a spot light beam exposure means, in which the medium is main/sub-scanned by a spot light beam, such as a laser beam, and a linear light beam exposure means, in which the medium is sub-scanned by a linear light beam are described. For the linear light source, a light source comprising a plurality of light emitting spots disposed in a line is described as an example.
A linear light source comprising a plurality of LEDs disposed in an array is disclosed as one of the aforementioned linear light sources. (Refer to, for example, U.S. Laid-Open No. 20010025936.) LEDs are well suited for the light source used in the reading light exposure apparatus, because they have higher output efficiency for the input energy and are more economical than LDs or other similar devices.
When a linear light source comprising an array of LEDs is used for the reading light exposure apparatus, the image information recorded on a medium is read out by converging light beams emitted from the LEDs on the medium in a straight line through cylindrical lenses disposed in parallel to the arranging direction of the LEDs and scanning the medium with the converged light beam. Typically, the reading performance of the reading light exposure apparatus is dependent on the profiles of the linearly converged light beam, particularly on the intensity and half-beam width of the light beam. It is preferable that the intensity be as high as possible and the half-beam width as narrow as possible.
FIG. 10 shows a typical conventional linear light source 1 comprising a plurality of surface emitting LED chips 10 disposed in a straight line. Each of the LED chips 10 has bonding pad sections 12 for direct bonding of wires to the electrodes of the chip and emission regions 13 which emit light when a current flows between the electrodes, and the bonding pad sections 12 are connected to a power supply (not shown) through an Au wire 11. Also, a utilization area 19 is defined by a slit (not shown) in order to narrow down the half-beam width of the reading light at the converging point. That is, the light beams radiated through the utilization area 19 are converged and used as the reading light.
The aforementioned linear light source 1, however, has a disadvantage that most of the utilization area 19 is occupied by non-emission regions, including the bonding pad sections 12, so that it is difficult to obtain reading light having sufficient intensity. Larger utilization area provides a stronger reading light, but at the same time, the half-beam width of the light at the converging point also becomes broader.
An LED chip having a non-emission region in the center is sometimes used for constructing a linear light source, but it also has similar disadvantage described above.